Project Abstract Despite high immunization rates among children, pertussis rates have been steadily increasing since 1980. Much of the increase has been among adolescents and adults. However, the highest rates of complications, hospitalizations, and deaths are among infants who have not yet completed their Diphtheria, tetanus and pertussis (Dtap) immunization series. Parents, specifically mothers, are cited as the most common source of infection in infants due to waning immunity in adults. A Healthy People 2020 goal is to immunize 80% of pregnant women for pertussis. However, Tetanus diphtheria (Td) with pertussis (Tdap) coverage remains less than 50% among pregnant and delivering women and even lower among those who are Medicaid recipients (14.3%). While Medicaid coverage should reduce racial/ethnic disparities in health outcomes among low- income populations by creating equal access to care, evidence has shown that racial and ethnic disparities persist in tertiary care access, such as immunization, among Medicaid and Medicare recipients, pregnant women and children. Tdap receipt was higher among publicly insured non-Hispanic (NH) Whites (17.6%) compared to publicly insured NH Blacks (8.4%) and publicly insured Hispanic (15.3%).Very few studies have examined individual-level factors related to Tdap receipt among pregnant women and even fewer have examined racial and ethnic differences in Tdap receipt. Past studies have not examined how birthing facility characteristics are associated with the receipt of Tdap among pregnant women and whether racial and ethnic differences in immunization rates are associated with birthing facility characteristics. The purpose of this study is three-fold: 1) to examine, using a probabilistic linkage between the state of Louisiana Medicaid enrollment and claims and birth certificate records, racial and ethnic disparities in Tdap receipt, first using the Institute of Medicine (IOM) definition of disparities (e.g., adjusting for health status indicators), then using The Agency for Healthcare Research and Quality (AHRQ) method which defines disparity as the total difference between racial /ethnic groups and the residual direct effect (RDE) which defines disparity as the difference after controlling for many factors such as socioeconomic status (SES), and health status indicators such as age, and gender. 2) to examine differences in Tdap receipt and timing of Tdap receipt (prenatal vs. postpartum) among women delivering in birthing facilities with different characteristics, overall and stratified by race/ethnicity and language preference. and 3) to examine using hierarchical modeling, the association between birthing hospital characteristics and racial/ethnic and language disparities in Tdap receipt among women with a Medicaid paid delivery and to see if certain birthing facility characteristics are associated with disparities in Tdap receipt.